(1) Field of the Invention
The present invention relates to an image defect correction apparatus that processes luminance signals output from two-dimensionally arranged light-sensitive elements via a plurality of vertical CCDs (Charge Coupled Devices) and one or more horizontal CCDs in a predetermined order, and outputs image information, and in particular to a technology for making less prominent a white line or a white defect on the displayed image that is generated from a point defect in a vertical CCD.
(2) Description of the Related Art
Imaging apparatuses, including home video cameras and digital still cameras, have come into wide use in recent years.
Some imaging apparatuses use a solid-state image sensing device, in which two-dimensionally arranged light-sensitive elements receives light and outputs luminance signals, and the luminance signals are output in a predetermined order via a plurality of vertical CCDs (Charge Coupled Devices) and one or more horizontal CCDS.
Meanwhile, such a solid-state image sensing device can represent as many as several hundreds to several thousands of pixels, and it is inevitable that a certain ratio of manufactured semiconductor wafers have substrate defects.
For the above reasons, if each manufactured product having at least one point defect were regarded as a defective product in the mass production, the yield rate would decrease prominently, and it would raise production cost. In actuality, therefore, to suppress the production cost, the standard for the defective product is relaxed so that the yield rate increases to a satisfactory level.
For example, in the mass production of solid-state image sensing devices representing approximately 500,000 pixels, a product of a solid-state image sensing device having two or three point defects in the light-sensitive elements or vertical CCDs are regarded as a conforming article.
It should be noted here that in general, a point defect in the light-sensitive elements is displayed as a white point on a displayed image, where a corresponding luminance signal always indicates a high luminance level regardless of the amount of light received.
As one example of such conventional technologies, Japanese Laid-Open Patent Application No. 2,565,261 discloses an image defect correction apparatus that stores data indicating (i) a position of a defective pixel of the solid-state image sensing device and (ii) the level of a defective component of the output signal, and corrects the defect with reference to the charge storage time.
In general, when a vertical CCD includes one point defect, all the luminance signals that pass through the point defect have high luminance levels and form a vertical line on the displayed image.
On the other hand, many of the recent imaging apparatuses have both a video shooting function and a still image shooting function, or a blur-by-hand correction function.
Japanese Laid-Open Patent Application No. 07-38799 discloses an imaging system that achieves a blur-by-hand correction function without either a deterioration of the resolution or an increase in the apparatus size or power consumption, as well as a conventional imaging system.
If a point defect is created in a light-sensitive element, an inconspicuous white point is displayed in an image. On the other hand, if a point defect is created in a vertical CCD, a vertical white line is displayed in a displayed image. Since the vertical white line is prominent, it is desirable that any correction is made to make the line inconspicuous.
In the case of a white point generated due to a point defect in a light-sensitive element, the white point can be corrected to a level where the white point becomes invisible to human eyes, by replacing pixel data of the white point with data of the surrounding pixels. This is applicable to a certain number of such point defects per product.
However, the method of replacing data of a pixel with data of the surrounding pixels cannot be applied to a white line that is displayed due to a point defect created in a vertical CCD. This is because the correction by the method substantially reduces the resolution in the horizontal direction, and as the number of pixels for correction increases, the corrected pixels become noticeable.
Meanwhile, a transfer of luminance signals includes what is called a transfer stop period during which the transfer of luminance signals from the light-sensitive elements to the vertical CCDs is stopped. The transfer stop period is, for example, two or three times the normal transfer time. If there is a point defect in a vertical CCD, output luminance signals corresponding to the point defect have values that have been increased in proportionate to the length of the transfer stop period. This generates what is called a white defect on the displayed screen that is a prominent white point and is the largest among the pixels on the vertical white line.
Also, when a still image is shot or a blur-by-hand correction function is performed to decrease the deterioration of resolution, a high-speed sweeping emission, in which luminance signals are output at a high speed, may be performed. The transfer time in the high-speed sweeping emission is, for example, one tenths the normal transfer time. Accordingly, if there is a point defect in a vertical CCD, the value of a luminance signal output in the high-speed sweeping emission is one tenths the value of a luminance signal output during the normal transfer time.
As understood from the above description, although the values of luminance signals corresponding to a vertical white line on the screen are higher than the other portions of the screen, the values are not necessarily even. That means it is desirable that a method of correcting the image defect on the screen can deal with different values of luminance signals for each vertical white line on the screen.